This invention relates to vent valves which are utilised in pipelines for releasing of air and other gases from the pipeline in order to prevent the formation of air pockets at high points along a pipeline which would otherwise restrict the flow of water through the pipeline. In particular the invention relates to those valves which are known as combined air release valves which are designed to vent or admit large quantities of air whilst the pipeline is being filled and emptied and to continuously release small amounts of air which accumulate in the pipeline in use.
Several types of air release valves are known. The first type commonly termed an automatic air release valve releases air which is accumulated under pressure in a pipeline during normal operating conditions. In this type of valve a float member is located within a housing which is mounted at its lower end to a pipeline which is to be vented by the valve member. The housing is provided at its upper end with venting aperture. During normal operation with the flow of water through the pipeline, water enters the housing which bouys the float member upwardly against the outlet aperture to seal the outlet aperture. However, when air migrates into the housing from the pipeline water is displaced out of the housing causing the float member to be displaced downwardly by gravity thereby opening the outlet aperture and allowing the air to vent. In this type of valve the dimensions of the venting aperture are small as the mass of the float must be greater than the force created by the working pressure which is operating on the orifice area.
A second type of vent valve commonly called combined air release valves employ a second substantially larger float member and a second substantially larger venting orifice in addition to the automatic float member and venting orifice in one common housing. Examples of this form of valve are disclosed in AU-B-68847. This type of valve allows large quantities of air to be vented from or admitted to the pipeline during filling or draining of the pipeline and also permit the continuous release of air under pressurised conditions. Some combined air release valves, commonly termed dynamic valves, are constructed such that the larger float member is lifted by the pressure differential caused by out rushing of air thereby closing the larger orifice in order to reduce the velocity of the air flow from the pipeline and thus the velocity of water flow into the valve. An example of such a device is disclosed in U.S. Pat. No. 5,511,577 and is marketed under the trade mark VENT-O-MAT. Other combined air release valves, commonly termed kinetic valves, are constructed such that the larger float member is unaffected by the out rushing air and only closes when buoyed by the entry of water into the housing. A form of this form of valve is disclosed in AU-B-76200/87 which is marketed under the trade mark BARAK. In both forms of construction the larger float member remains in sealing engagement with the venting orifice whilst the valve is pressurised and will only reopen once pressure in the housing has dropped to atmospheric pressure, and as a result the air may only be vented through the small orifice during the pressurised operation.
A disadvantage of vent valves of the form described above is that due to the small dimensions of the small orifice, buoyant foreign matter present in the water can block the orifice causing the valve to leak. In addition a disadvantage of the dynamic type of valve is that the large orifice closes before completion of the venting and residual air in the pipeline may be swept past the valve due to the inability of the small orifice to cope with the volume of air to be vented resulting in the formation of air pockets along the pipeline which will restrict the flow of water in the pipeline. A disadvantage of the kinetic type of valve is that the valve closes suddenly causing adverse pressure changes to occur in the pipeline as a result of such closure which can often result in damage to the pipeline.
Accordingly, the invention resides in a pipeline vent valve comprising a body defining a chamber having an inlet towards its lower end which is adapted to be connected to a pipeline and an outlet towards its upper end, the outlet defined by a valve seat, a first valve member supported in the chamber to be moveable between a first position at which it is in sealing engagement with the valve seat and a second position at which it is out of engagement with the valve seat, said first valve member in its movement to the first position being responsive to the magnitude of the gaseous flow rate through the valve seat to be moveable to the first position on the gaseous flow rate exceeding a desired level, said first valve member also being responsive to the level of liquid in the chamber and being adapted to close when the liquid level in the chamber exceeding a predetermined level, said first valve member having an opening providing communication to each side of the first valve member, a second valve member fixed to the first valve member to be moveable between a first position at which it is in sealing engagement with the entry of said opening and a second position at which it is out of engagement with the entry of said opening, a float member supported within the chamber and fixed to said second valve member to cause movement of the second valve member between the first and second position as a result of movement of the valve member resulting from the presence of liquid in the chamber.
According to a preferred feature of the invention said second valve member in its movement from the second to first position will variably engage the entry whereby the degree of closure of the entry will increase as the valve member approaches the first position.
According to one embodiment of the invention the opening has a divergent cross section and the second valve member comprises a flexible membrane fixed at one end adjacent to the most divergent portion of the opening whereby on the movement of the second valve member to the first position the second valve member increasingly engages the entry of the opening from the most divergent portion of the opening to the most convergent.
According to a further preferred feature of the invention the first valve member is hingedly supported from the body at a position adjacent to the valve seat, said hinge resiliently biasing the first valve member to the first position.
According to a alternative preferred feature of the invention the first valve member comprises a buoyant member located within the chamber.
According to a further preferred feature of the invention the body accommodates a bearing member having a portion located exterior of the body and a second portion located within the chamber, said second portion being engageable with the float member whereby on manipulation of the first portion the float member can be moved within the chamber to cause the second valve member to move from its first position.
The invention will be more fully understood in the light of the following description of several specific embodiments.